/****************************************************************************
 *
 * Copyright 2016 Samsung Electronics All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
 * either express or implied. See the License for the specific
 * language governing permissions and limitations under the License.
 *
 ****************************************************************************/
/****************************************************************************
 * fs/dirent/fs_seekdir.c
 *
 *   Copyright (C) 2007, 2008, 2011, 2014 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <tinyara/config.h>

#include <sys/types.h>
#include <dirent.h>
#include <errno.h>

#include <tinyara/fs/fs.h>
#include <tinyara/fs/dirent.h>

#include "inode/inode.h"

/****************************************************************************
 * Private Functions
 ****************************************************************************/

/****************************************************************************
 * Name: seekpseudodir
 ****************************************************************************/

static inline void seekpseudodir(struct fs_dirent_s *idir, off_t offset)
{
	struct inode *curr;
	struct inode *prev;
	off_t pos;

	/* Determine a starting point for the seek.  If the seek
	 * is "forward" from the current position, then we will
	 * start at the current poisition.  Otherwise, we will
	 * "rewind" to the root dir.
	 */

	if (offset < idir->fd_position) {
		pos = 0;
		curr = idir->fd_root;
	} else {
		pos = idir->fd_position;
		curr = idir->u.pseudo.fd_next;
	}

	/* Traverse the peer list starting at the 'root' of the
	 * the list until we find the node at 'offset".  If devices
	 * are being registered and unregistered, then this can
	 * be a very unpredictable operation.
	 */

	inode_semtake();
	for (; curr && pos != offset; pos++, curr = curr->i_peer) ;

	/* Now get the inode to vist next time that readdir() is called */

	prev = idir->u.pseudo.fd_next;
	idir->u.pseudo.fd_next = curr;	/* The next node to visit (might be null) */
	idir->fd_position = pos;	/* Might be beyond the last dirent */

	if (curr) {
		/* Increment the reference count on this next node */

		curr->i_crefs++;
	}

	inode_semgive();

	if (prev) {
		inode_release(prev);
	}
}

/****************************************************************************
 * Name: seekmountptdir
 ****************************************************************************/

#ifndef CONFIG_DISABLE_MOUNTPOINT
static inline void seekmountptdir(struct fs_dirent_s *idir, off_t offset)
{
	struct inode *inode;
	off_t pos;

	/* Determine a starting point for the seek.  If the seek
	 * is "forward" from the current position, then we will
	 * start at the current poisition.  Otherwise, we will
	 * "rewind" to the root dir.
	 */

	inode = idir->fd_root;
	if (offset < idir->fd_position) {
		if (inode->u.i_mops && inode->u.i_mops->rewinddir) {
			/* Perform the rewinddir() operation */

			inode->u.i_mops->rewinddir(inode, idir);
			pos = 0;
		} else {
			/* We can't do the seek and there is no way to return
			 * an error indication.
			 */

			return;
		}
	} else {
		pos = idir->fd_position;
	}

	/* This is a brute force approach... we will just read
	 * directory entries until we are at the desired position.
	 */

	while (pos < offset) {
		if (!inode->u.i_mops || !inode->u.i_mops->readdir || inode->u.i_mops->readdir(inode, idir) < 0) {
			/* We can't read the next entry and there is no way to return
			 * an error indication.
			 */

			return;
		}

		/* Increment the position on each successful read */

		pos++;
	}

	/* If we get here the directory position has been successfully set */

	idir->fd_position = pos;
}
#endif

/****************************************************************************
 * Public Functions
 ****************************************************************************/

/****************************************************************************
 * Name: seekdir
 *
 * Description:
 *   The seekdir() function sets the location in the directory stream from
 *   which the next readdir() call will start.  seekdir() should be used with
 *   an offset returned by telldir().
 *
 * Inputs:
 *   dirp -- An instance of type DIR created by a previous
 *     call to opendir();
 *   offset -- offset to seek to
 *
 * Return:
 *   None
 *
 ****************************************************************************/

void seekdir(FAR DIR *dirp, off_t offset)
{
	struct fs_dirent_s *idir = (struct fs_dirent_s *)dirp;

	/* Verify that we were provided with a valid directory structure,
	 * A special case is when we enumerate an "empty", unused inode (fd_root
	 * == 0).  That is an inode in the pseudo-filesystem that has no
	 * operations and no children.  This is a "dangling" directory entry that
	 * has lost its children.
	 */

	if (!idir || !idir->fd_root) {
		return;
	}

	/* The way we handle the readdir depends on the type of inode
	 * that we are dealing with.
	 */

#ifndef CONFIG_DISABLE_MOUNTPOINT
	if (INODE_IS_MOUNTPT(idir->fd_root)) {
		/* The node is a file system mointpoint */

		seekmountptdir(idir, offset);
	} else
#endif
	{
		/* The node is part of the root pseudo file system */

		seekpseudodir(idir, offset);
	}
}
